JPH05312109A - Exhaust gas control device of diesel engine - Google Patents

Abstract

PURPOSE:To maintain an HC/NOx density ratio in exhaust gas higher than a specified value and to realize a high reduction rate of NOx with a catalyst by restraining generation of NOx by way of circulating exhaust gas and increasing exhaust gas circulation at the time when catalyst temperature is high. CONSTITUTION:A means 10 to detect drive condition of an engine and an exhaust gas circulating passage are furnished, and an exhaust gas circulation control means 11 controls an exhaust gas circulating amount from the exhaust gas circulating passage in accordance with the drive condition of the engine. A catalyst capable of reducing NOx in exhaust gas atmosphere of the diesel engine is interposed in the downstream of an exhaust gas passage, and a means 13 to detect catalyst temperature is provided. Additionally, an exhaust gas density estimating means 14 to estimate density of HC and density of NOx in exhaust gas from the drive condition of the engine is provided. In the case when the catalyst temperature is higher than a specified value, an exhaust gas circulation amount from the exhaust gas circulating passage is increased and corrected so that a density ratio of HC and NOx in exhaust gas becomes higher than a specified value. Consequently, it is possible to precisely and correctly reduce NOx.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust control device for a diesel engine.

[0002]

2. Description of the Related Art In order to reduce NOx emitted from a diesel engine, an exhaust gas recirculation device (EGR device) is provided for recirculating a part of exhaust gas from an exhaust passage into intake air. However, it is not always sufficient to reduce NOx.

On the other hand, a catalyst capable of reducing NOx even in an exhaust gas atmosphere in which oxygen exists, such as a diesel engine, has been developed. In this case, at Hokkaido University, etc.,
A method for improving the NOx reduction rate by injecting fuel into exhaust gas and using fuel (HC) as a reducing agent has been reported (see Nikkan Kogyo Shimbun, September 20, 1990, etc.).

[0004]

However, even if such a catalyst is used, in this case, in addition to the engine, a fuel injection device is provided in the exhaust pipe and the fuel is directly injected into the exhaust gas.
The system becomes complicated and the cost increases significantly.

Further, since fuel consumption as a reducing agent deteriorates fuel efficiency, in order to inject fuel into exhaust gas,
The exhaust pipe becomes hot and heat deterioration cannot be avoided.

An object of the present invention is to accurately reduce NOx by controlling exhaust gas without causing such a problem.

[0007]

A first aspect of the present invention is to provide a means 10 for detecting engine operating conditions as shown in FIG. 1 and an exhaust gas recirculation passage for recirculating a part of exhaust gas from the engine exhaust passage to an intake system. And the exhaust gas recirculation control means 1 based on the operating conditions of the engine.
In a diesel engine 1 for controlling the amount of exhaust gas recirculation from the exhaust gas recirculation passage, a catalyst 12 capable of reducing NOx in the exhaust gas atmosphere of the diesel engine is provided downstream of the exhaust passage, and means 13 for detecting the catalyst temperature. And an exhaust gas concentration estimating means 14 for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine, and the concentration ratio of HC and NOx in the exhaust is a predetermined value when the catalyst temperature is a predetermined value or more. As described above, the exhaust gas recirculation correction control means 15 for increasing and correcting the amount of exhaust gas recirculation from the exhaust gas recirculation passage is provided.

A second aspect of the invention is a means 20 for detecting engine operating conditions as shown in FIG. 2, an injection timing control means 21 for controlling the fuel injection timing of a fuel injection pump based on the engine operating conditions, and an engine. In a diesel engine including an exhaust gas recirculation passage that recirculates a part of the exhaust gas from the exhaust gas recirculation passage to the intake system, and an exhaust gas recirculation control unit 22 that controls the amount of exhaust gas recirculation from the exhaust gas recirculation passage based on the operating conditions of the engine, Means 2 for interposing a catalyst 23 capable of reducing NOx in the exhaust atmosphere of a diesel engine downstream of the exhaust passage and detecting the catalyst temperature
4 and the operating conditions of the engine, the concentration of HC in the exhaust gas and NOx
Of the exhaust gas concentration estimating means 25 for estimating the concentration of the exhaust gas and the fuel injection timing of the fuel injection pump so that the concentration ratio of HC and NOx in the exhaust gas becomes a predetermined value or more when the catalyst temperature is a predetermined value or more. An injection timing correction control means 26 for correcting the angle is provided.

A third aspect of the invention is a means 30 for detecting the operating condition of the engine as shown in FIG. 3, an injection timing control means 31 for controlling the fuel injection timing of the fuel injection pump based on the operating condition of the engine, and a fuel. An injection rate variable mechanism 32, an exhaust gas recirculation passage for recirculating a part of the exhaust gas from the engine exhaust passage to the intake system
In a diesel engine equipped with an exhaust gas recirculation control means 33 for controlling the amount of exhaust gas recirculation from the exhaust gas recirculation passage based on operating conditions of the engine, a catalyst capable of reducing NOx in the exhaust atmosphere of the diesel engine downstream of the exhaust passage. 34 for interposing 34, for detecting the catalyst temperature, exhaust concentration estimating means 36 for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine, and the case where the catalyst temperature is above a predetermined value. Further, the injection correction control means 3 for correcting the fuel injection timing of the fuel injection pump and retarding the fuel injection rate so that the concentration ratio of HC and NOx in the exhaust becomes a predetermined value or more.
7 and are provided.

[0010]

[Function] The exhaust gas recirculation suppresses the generation of NOx,
When the exhaust gas recirculation amount is increased, HC increases. Further, HC is increased by retarding the fuel injection timing or by reducing the fuel injection rate.

On the other hand, NO in the exhaust atmosphere containing oxygen
The catalyst capable of reducing x is activated when the temperature is high, and is NO when the HC / NOx concentration ratio in the exhaust gas is equal to or higher than a predetermined value.
The reduction rate of x becomes high.

That is, in the first aspect of the present invention, the exhaust gas recirculation suppresses the generation of NOx, and the exhaust gas recirculation amount is increased when the catalyst temperature is high, so that the HC / NOx concentration ratio in the exhaust gas becomes equal to or higher than a predetermined value. Hold, which results in a high reduction rate of NOx on the catalyst.

According to the second aspect of the invention, the NO is also used in the exhaust gas recirculation.
By suppressing the generation of x and retarding the fuel injection timing of the fuel injection pump, the HC / NOx concentration ratio in the exhaust gas is maintained at a predetermined value or higher, and a high reduction rate of NOx in the catalyst is obtained.

In the third aspect of the present invention, similarly, the exhaust gas recirculation suppresses the generation of NOx, and the fuel injection timing of the fuel injection pump is retarded and the fuel injection rate is reduced, whereby the HC / NOx concentration ratio in the exhaust gas is set to a predetermined value. Keep above the value, N in the catalyst
A high reduction rate of Ox is obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 and FIG. 5 show an exhaust gas recirculation device 50 and a catalyst (zeolite catalyst) 51 capable of reducing NOx in an exhaust gas atmosphere in which oxygen exists.

Reference numeral 52 is an exhaust passage of the engine, 53 is an intake passage of the engine, 54 is an exhaust gas recirculation passage branching from the exhaust passage 52 and connected to the intake passage 53, and 55 is an exhaust gas interposed in the middle of the exhaust gas recirculation passage 54. A recirculation valve, 56 is a negative pressure control valve that controls the operating negative pressure of the exhaust recirculation valve 55, and 57 is an intake throttle valve provided in the intake passage 53 upstream of the confluence portion of the exhaust recirculation passage 54.

The negative pressure control valve 56 includes a lower diaphragm valve portion 58 for performing basic negative pressure control according to exhaust pressure, and an upper portion for changing its control characteristic to a desired characteristic as a variable control mechanism. It is roughly divided into a step motor 59.

The diaphragm valve portion 58 includes a casing 60.
Mainly the diaphragm 61 arranged inside,
With this diaphragm 61, an exhaust pressure chamber 62 is formed at the bottom.
The intake pressure chambers 63 are formed in the upper part.

A predetermined set load is applied to the diaphragm 61 by a set spring 64 arranged in a compressed state in the exhaust pressure chamber 62, and a valve body 65 is attached to the intake pressure chamber 63 side. ..

The intake pressure chamber 63 communicates with an intake passage 53 upstream of the intake throttle valve 57 via an intake pressure passage 66. In the intake pressure chamber 63, the intake introduction port 6 is opposed to the valve body 65.
7 is formed, and the intake introduction port 67 is connected to the negative pressure passage 6
It communicates with 8.

The step motor 59 includes a pair of stators 70 fixed to a casing 69 and bearings 71 and 7.
The rotor 73 is rotatably supported by the rotor 73. The step motor 59 has a rotation angle controlled stepwise by applying a predetermined pulse signal to the coil of the stator 70. For example, the rotor 7 is rotated in four steps.
3 is configured to rotate once. The rotor 73 has a cylindrical shape, and an internal thread 74 is formed on the inner peripheral surface thereof.

Reference numeral 75 denotes a guide member fixed to the inner peripheral side of the bearing 72 of the casing 69, and reference numeral 76 denotes a plunger guided by the guide member 75 so as to be non-rotatable and slidable in the axial direction. 77 is formed, and this is screwed into the female screw 74 of the rotor 73.

This plunger 76 has a step motor 5
It is configured to linearly move in the axial direction in accordance with the rotation angle of 9, and is located on the center line of the diaphragm 61. A disk-shaped spring seat 78 is provided below the plunger 76.
Is fixed, and the tip of the plunger 76 penetrates the spring seat 78 and projects downward by a predetermined amount.

Reference numeral 79 denotes an intermediate member for transmitting the operation of the plunger 76 to the diaphragm 61. The intermediate member 79 includes a disk-shaped spring seat portion 79a and a push rod portion 79b extending from one side portion of the spring seat portion 79a in the axial direction of the plunger 76, and the push rod portion 79b is provided in the intake pressure chamber of the casing 60. 63 is provided so as to penetrate the upper surface portion.

An auxiliary spring 80 is disposed in a compressed state between the spring seat portion 79a and the spring seat 78, and the urging force causes the tip of the push rod portion 79a of the intermediate member 79 to move to the retainer 81 on the diaphragm 61. Pressed.

The biasing force of the auxiliary spring 80 becomes weaker when the step motor 59 rotates and the spring seat 78 moves upward, and conversely becomes stronger when the spring seat 78 moves downward. FIG. 6 shows the relationship between the number of steps of the step motor 59 and the set load of the auxiliary spring 80.

The exhaust gas recirculation valve 55 provided in the middle of the exhaust gas recirculation passage 54 is a diaphragm type valve, and its negative pressure chamber 82 is provided.
A signal negative pressure, for example, a negative pressure from a vacuum tank of the engine is introduced into the negative pressure passage 83 through the negative pressure passage 83.

The negative pressure passage 83 is connected to the negative pressure passage 68 of the negative pressure control valve 56, and the negative pressure control valve 56 appropriately introduces intake air to dilute the signal negative pressure, whereby the exhaust gas recirculation valve. The opening degree of 55 is controlled.

Exhaust gas recirculation valve 55 Exhaust gas recirculation passage 54 on the downstream side
Is provided with an orifice 84 on the confluence side of the intake passage 53 (intake manifold), and the exhaust pressure between the exhaust gas recirculation valve 55 and the orifice 84 is exhausted through the exhaust pressure passage 85 to the exhaust pressure of the negative pressure control valve 56. It is introduced into the chamber 62.

The intake throttle valve 57 of the intake passage 53 controls a particularly large amount of exhaust gas recirculation by narrowing the area of the intake passage, and its opening degree is controlled by the step motor 86.

The negative pressure control valve 56 in FIG. 5 shows a state in which the number of steps of the step motor 59 is at an appropriate intermediate value, and a differential pressure between exhaust pressure and intake pressure acts on the diaphragm 61, and It is biased in the closing direction by the set spring 64 and in the opening direction by the auxiliary spring 80.

When the urging force of the auxiliary spring 80 is weakened, the valve body 65 moves toward the closing side of the intake air intake port 67, and the intake air intake amount from the intake air intake port 67 to the negative pressure passage 83 decreases. When the opening degree of the return valve 55 decreases and the biasing force of the auxiliary spring 80 is increased, the valve body 65 moves to the opening side of the intake introduction port 67, and the intake introduction amount from the intake introduction port 67 to the negative pressure passage 83 is reduced. With the increase, the opening degree of the exhaust gas recirculation valve 55 increases.

That is, the step motor 5 of the negative pressure control valve 56
The opening / closing characteristics of the exhaust gas recirculation valve 55 can be controlled by controlling the rotation angle of the exhaust gas recirculation valve 55, and thereby the opening angle control of the intake throttle valve 57 via the step motor 86 and the rotation angle control of the step motor 59 of the negative pressure control valve 56 can be performed. The exhaust gas recirculation amount characteristic can be obtained.

When the exhaust pressure becomes high for some reason, the valve body 65 of the negative pressure control valve 56 moves to the closed side of the intake introduction port 67, and the opening degree of the exhaust gas recirculation valve 55 decreases. The amount of reflux does not become excessive. Also,
Since the intake pressure is guided to the negative pressure control valve 56, the exhaust gas recirculation valve 55 can be controlled even in an engine with a supercharger, and predetermined exhaust gas recirculation can be performed.

The catalyst 51 capable of reducing NOx in the exhaust atmosphere containing oxygen is installed in the exhaust passage 52 at the downstream side of the branch portion of the exhaust gas recirculation passage 54.

The catalyst 51 maintains a high NOx reduction rate when the HC / NOx concentration ratio in the exhaust gas is equal to or higher than a predetermined value. Specifically, as shown in FIG. 32, HC / NO that can obtain a value of about 10% required for the NOx reduction rate.
The x concentration ratio is 0.5, and above this, the reduction rate is improved until the HC / NOx concentration ratio = 3 or less. HC / NO
When the x concentration ratio exceeds 3, the drivability of the engine becomes unsatisfactory. Therefore, by controlling the HC / NOx concentration ratio between 0.5 and 3, a high NOx reduction rate can be maintained.

FIG. 7 shows a column-type fuel injection pump 90 for injecting fuel into the engine. The plunger 92 moves up and down by the rotation of the cam 91 driven by the engine, and the fuel in the pressurizing chamber 93 is passed through the fuel valve 94. Then, it is pressure-fed to the injection nozzle 100.

A control sleeve 9 is provided around the plunger 92.
5 is mounted, and the position of the sleeve 95 determines the start time of fuel pressure feeding.

The sleeve 95 opens and closes the opening to the fuel chamber side of the passage 97 provided in the plunger 92 which communicates between the fuel chamber 96 into which the fuel is fed and the pressurizing chamber 93, and the process in which the plunger 92 rises. Then, when the opening of the passage 97 is closed by the lower end of the sleeve 95, the communication with the fuel chamber 96 is cut off, the pressure in the pressurizing chamber 93 starts to increase, and the fuel is pumped.

When the plunger 92 rises and the port 97a branching from the passage 97 communicates with the opening 95a provided in the middle of the sleeve 95, the pressurizing chamber 93 is restored to the fuel chamber 96 again.
The fuel pumping is terminated by communicating with the.

By moving the position of the sleeve 95 up and down by the position control mechanism 98, it is possible to advance or delay the fuel pumping start timing.

Further, since the branch port 97a is opened as an inclined groove around the plunger, by changing the rotational position of the plunger 92 around the axis by the rotation control mechanism 99, the timing of communication with the passage 95a changes. It is possible to change the end time of the fuel pumping.

That is, the rotation control mechanism 99 controls the fuel injection timing, and the position control mechanism 98 controls the fuel injection amount.

FIGS. 8 and 9 show a variable mechanism 101 for changing the oil feed rate (fuel injection rate) by advancing and retarding the phase of the cam 91 of the fuel injection pump 90.

This is interposed in the connecting portion between the pump shaft (cam shaft) 90a of the fuel injection pump 90 and the rotating body 102 to which the engine rotation is transmitted, and the transmission phase of the engine rotation with respect to the pump shaft 90a is variably changed. adjust.

Rotating disk 1 coaxially coupled to pump shaft 90a
On the shaft portion 103 of 04, the rotating body 102 can freely rotate with this.
Is supported.

Then, in order to impart a phase difference to the rotation transmitted from the rotating body 102 to the turntable 104,
As a mechanism for connecting the rotary disc 104 and the rotary body 102 so as to be relatively displaceable in the rotation (circumferential) direction, first of all, the rotary disc 104 has a pair of circular holes 104a equidistant from the center of rotation.
Is opened, and the first eccentric cam 105 is inserted therein. Also, a circular hole 105a provided in the eccentric cam 105
The second eccentric cam 106 is inserted in the.

Eccentric pin 106b of the second eccentric cam 106
Penetrates into the rotating body 102 from the side surface, and the eccentric pin 105b of the first eccentric cam 105 is connected to the piston 107a housed in the cylinder 107.

The cylinder 107 is integrally attached to the turntable 104 in the radial direction of the shaft 103, and has an oil chamber 107b.
The pressure oil supplied through the inner peripheral passage 103a of the shaft portion 103 is guided to. The piston 107a moves to a position where this supply pressure is balanced with the return spring 107c.

Therefore, the first eccentric cam 105 is rotated by the eccentric pin 105b according to the position of the piston 107a, which causes the second eccentric cam 106 to rotate.
With respect to the rotating body 102 and the rotating plate 104, which are displaced in the circumferential direction and connected via the eccentric pin 106b, change the phase in the rotating direction.

As a result, the rotational phase of the pump shaft 90a of the fuel injection pump 90, that is, the cam 91, changes with respect to the engine rotation, and the fuel feed rate changes according to the lift characteristics of the cam 91.

The oil pressure from the oil pump 109 guided to the oil chamber 107b of the cylinder 107 changes according to the opening of the control valve 108. When the control valve opening increases, the oil pressure decreases and the rotational phase of the cam 91 changes. If the control valve opening degree is delayed, the hydraulic pressure rises and the rotational phase of the cam 91 advances.

That is, when the opening degree of the control valve 108 is increased, the oil feeding rate and the injection rate are reduced, and when it is decreased, the oil feeding rate and the injection rate are increased.

FIG. 10 shows exhaust gas recirculation control means, exhaust gas concentration estimation means, exhaust gas recirculation correction control means (first invention), injection timing control means, exhaust gas recirculation control means, exhaust gas concentration estimation means, injection timing correction control means (first embodiment). 2 invention), injection timing control means,
Control unit 120 as exhaust gas recirculation control means, exhaust gas concentration estimation means, injection correction control means (third invention)
It is a block diagram showing.

The control unit 120 includes a central processing unit (CPU) 121 and a read only memory (RO).
M) 122, random access memory (RAM) 12
3, an input / output circuit (I / O) 124.

The I / O 124 includes an engine speed sensor 125, an accelerator opening sensor 126, and an intake air temperature sensor 12.
7, the output of the exhaust temperature sensor 128, the intake pressure sensor 129, the water temperature sensor 130 that detects the cooling water temperature, the fuel temperature sensor 131, the catalyst temperature sensor 132 that detects the temperature of the catalyst 51, etc. are input.

The CPU 121 fetches the information from the I / O 124 according to the program stored in the ROM 122, processes it, and calculates the fuel injection amount, the fuel injection timing, the fuel injection pump 90 for controlling the fuel injection rate, and the exhaust gas recirculation amount. Data, which is a control amount for controlling the intake throttle valve 57 and the negative pressure control valve 56 to be controlled, is set in the I / O 124. The RAM 123 is used to temporarily save the data related to the arithmetic processing of the CPU 121.

The I / O 124 is based on the data from the CPU 121, and the fuel injection pump 90 (position control mechanism 98,
Each actuator of the rotation control mechanism 99, variable mechanism 101
Control valve 108), intake throttle valve 57 (step motor 8
6) Output a control signal to the negative pressure control valve 56 (step motor 59).

Intake throttle valve 57 for obtaining the basic fuel injection amount, fuel injection timing, exhaust gas recirculation amount, and exhaust gas recirculation amount.
11 to FIG. 15 show the characteristics of the basic opening degree and the basic step number of the step motor 59 of the negative pressure control valve 56.

Next, the control contents of the control unit 120 will be described with reference to the flowchart.

FIG. 16 corresponds to the first aspect of the invention. First, at step 100, various data of operating conditions such as engine speed Ne, accelerator opening Acc, cooling water temperature Tw, catalyst temperature Tt, etc. are read.

In step 110, the basic injection amount QN and the basic injection timing I are based on the data read in step 100.
TN, basic opening WN of intake throttle valve 57, negative pressure control valve 56
The basic step number STEPN of the step motor 59 is calculated.

The basic injection amount QN and the basic injection timing ITN are obtained by using the data of FIGS. 11 and 12 as the basic opening W of the intake throttle valve 57.
N, the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 is the data of FIG. 14 and FIG.
Store it in 2 and read it.

Next, in step 120, step 100
It is judged whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, eg 350 ° C.).

If it is determined in step 120 that the catalyst temperature is less than the predetermined value, the correction opening ΔW of the intake throttle valve 57 and the correction step number ΔSTEP of the step motor 59 of the negative pressure control valve 56 are determined in step 140. It is set to 0, that is, the basic exhaust gas recirculation amount is maintained, and the routine proceeds to step 150.

On the other hand, if it is determined in step 120 that the catalyst temperature is equal to or higher than the predetermined value, then in step 130, the HC concentration and NOx concentration in the exhaust gas are estimated from the operating conditions, and H
The correction opening degree ΔW of the intake throttle valve 57 and the correction step number ΔSTEP of the step motor 59 of the negative pressure control valve 56 are calculated so that the C / NOx concentration ratio becomes equal to or more than a predetermined value, that is, the increase amount of the exhaust gas recirculation is set. Then, the process proceeds to step 150.

Correction opening ΔW of intake throttle valve 57, correction step number ΔSTE of step motor 59 of negative pressure control valve 56
P is based on the engine speed Ne and the basic injection amount QN shown in FIG.
7, the data as shown in FIG. 18 is stored in the ROM 122 and is read.

Then, in step 150, QN, IT
From N, WN + ΔW, STEPN + ΔSTEP, fuel injection amount Q, injection timing IT, opening W of intake throttle valve 57, step number of step motor 59 of negative pressure control valve 56 STEP
And output.

With such a configuration, when the catalyst 51 has not reached the activation temperature, it is necessary to secure the flow rate of exhaust gas to the catalyst 51 in order to promote the activation of the catalyst 51.
The intake throttle valve 57 and the exhaust gas recirculation valve 55 are set to the basic opening degree based on the operating condition of the engine, and the exhaust gas recirculation is performed at the basic exhaust gas recirculation amount.

Therefore, the exhaust gas recirculation suppresses the generation of NOx, and in this case, the generated amount is small, and NOx is reduced.
Is sufficiently reduced.

On the other hand, when the catalyst 51 is at the activation temperature,
The opening degrees of the intake throttle valve 57 and the exhaust gas recirculation valve 55 are corrected so that the HC / NOx concentration ratio in the exhaust becomes equal to or higher than a predetermined value.
The exhaust gas recirculation amount is controlled to increase.

When the HC / NOx concentration ratio in the exhaust gas is equal to or higher than a predetermined value, a high NOx reduction rate by the catalyst 51 is obtained.

As the exhaust gas recirculation amount is changed, the NOx concentration and the HC concentration are increased / decreased according to the characteristics shown in FIGS. 19 and 20, so that by changing the exhaust gas recirculation amount, as shown in FIG.
The HC / NOx concentration ratio is arbitrarily set with the characteristic of 1.

That is, the engine speed Ne and the basic injection amount Q
Based on N, the opening degree of the intake throttle valve 57 and the exhaust gas recirculation valve 55 is controlled to control the exhaust gas recirculation amount, but the engine speed Ne,
The HC concentration and NOx concentration in the exhaust gas are estimated from the basic injection amount QN, and the increased amount of the exhaust gas recirculation amount is obtained. Therefore, based on the engine speed Ne and the basic injection amount QN, the intake throttle valve 5
7. By correcting the opening degree of the exhaust gas recirculation valve 55, HC /
The NOx concentration ratio is controlled to be a predetermined value or higher.

As a result, generation of NOx due to exhaust gas recirculation is suppressed, and a high reduction rate of NOx in the catalyst 51 is maintained, so that NOx is greatly reduced.

In this case, the reduction rate of NOx in the catalyst 51 is, as shown in FIG. 32, 0.5 ≦ HC / NO in exhaust gas
By increasing the exhaust gas recirculation amount such that the x concentration ratio ≦ 2 to 3, a high reduction rate is secured.

The opening correction amounts ΔW and ΔSTEP of the intake throttle valve 57 and the exhaust gas recirculation valve 55 are smaller as the basic injection amount QN is smaller (FIGS. 17 and 18), but the basic injection amount QN is smaller. This is because the basic exhaust gas recirculation amount is increased more and more (FIG. 13), and in this case, the shortage with respect to the predetermined HC / NOx concentration ratio is small.

Since the exhaust gas recirculation control is performed in this manner, NO
It is possible to increase HC while suppressing the generation of x, and there is a synergistic effect in setting the HC / NOx concentration ratio to a predetermined value. In addition, fuel efficiency is hardly deteriorated as compared with fuel injection into exhaust gas, control can be performed using conventional parts, the system is simplified, and cost is not increased.

Further, there is no problem in terms of durability due to fuel injection in the exhaust gas, and moreover, the HC / NOx concentration ratio can be controlled with high accuracy. By performing a large amount of exhaust gas recirculation, the amount of exhaust gas passing through the catalyst 51 decreases, and the catalyst 51
It is effective for increasing the temperature.

FIG. 22 corresponds to the second invention, in which the fuel injection timing is retarded and the HC / NOx concentration ratio in the exhaust gas is set to a predetermined value or more.

First, at step 200, the engine speed N
e, accelerator opening Acc, cooling water temperature Tw, catalyst temperature Tt
Read various data of operating conditions such as.

In step 210, the basic injection amount QN and the basic injection timing I are based on the data read in step 200.
TN, basic opening WN of intake throttle valve 57, negative pressure control valve 56
The basic step number STEPN of the step motor 59 is calculated.

The basic injection amount QN and the basic injection timing ITN are based on the data shown in FIGS. 11 and 12, and the basic opening WN of the intake throttle valve 57 and the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 are described above. 14 and 15 are stored in the ROM 122 and read.

Next, in step 220, step 200
It is judged whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, eg 350 ° C.).

If it is determined in step 220 that the catalyst temperature is less than the predetermined value, then step 240 is continued.
Proceed to.

On the other hand, when it is determined in step 220 that the catalyst temperature is equal to or higher than the predetermined value, in step 230, the HC concentration and NOx concentration in the exhaust gas are estimated from the operating conditions, and H
The correction injection timing opening ΔIT is calculated so that the C / NOx concentration ratio becomes equal to or greater than the predetermined value, and the routine proceeds to step 240.

As the corrected injection timing opening ΔIT, the data shown in FIG. 23 is stored in the ROM 122 based on the engine speed Ne and the basic injection amount QN, and this is read.

Then, in step 240, QN, ITN
From + ΔIT, WN, STEPN, the fuel injection amount Q, the injection timing IT, the opening W of the intake throttle valve 57, and the step number STEP of the step motor 59 of the negative pressure control valve 56 are obtained and output.

That is, while the generation of NOx is suppressed by the exhaust gas recirculation and the catalyst 51 is at the activation temperature, the fuel injection timing is retarded so that the HC / NOx concentration ratio in the exhaust gas becomes equal to or higher than a predetermined value. To be done.

When the fuel injection timing is changed, NOx
The concentration and the HC concentration are increased / decreased according to the characteristics shown in FIGS. 24 and 25. Therefore, by changing the fuel injection timing,
The HC / NOx concentration ratio is arbitrarily set with the characteristics shown in FIG.

Therefore, the retard amount of the fuel injection timing is obtained based on the engine speed Ne and the basic injection amount QN, and the fuel injection timing is corrected by the retard angle so that the HC / NOx concentration ratio is equal to or more than a predetermined value. Controlled by.

As a result, generation of NOx due to exhaust gas recirculation is suppressed, a high reduction rate of NOx in the catalyst 51 is maintained, and NOx is greatly reduced.

FIG. 27 corresponds to the third aspect of the invention, in which the fuel injection timing is retarded while the fuel injection rate is lowered to set the HC / NOx concentration ratio in the exhaust gas to a predetermined value or more.

First, at step 300, the engine speed N
e, accelerator opening Acc, cooling water temperature Tw, catalyst temperature Tt
Read various data of operating conditions such as.

In step 310, the basic injection amount QN and the basic injection timing I based on the data read in step 300.
TN, basic opening WN of intake throttle valve 57, negative pressure control valve 56
Of the step number 59 of the step motor 59 and the oil feed rate variable mechanism 101 for obtaining the basic fuel injection rate
The basic cam phase DQN of is calculated.

The basic injection amount QN and the basic injection timing ITN are based on the data shown in FIGS. 11 and 12, and the basic opening WN of the intake throttle valve 57 and the basic step number STEPN of the step motor 59 of the negative pressure control valve 56 are as described above. 14 and FIG. 15 of the above, the basic cam phase DQN is RO as shown in FIG.
It is stored in M122 and is read.

Next, in step 320, step 300
It is judged whether or not the catalyst temperature Tt read in is equal to or higher than a predetermined value (activation temperature, eg 350 ° C.).

If it is determined in step 320 that the catalyst temperature is less than the predetermined value, then step 340 is performed.
Proceed to.

On the other hand, when it is determined in step 320 that the catalyst temperature is equal to or higher than the predetermined value, in step 330, the HC concentration and NOx concentration in the exhaust gas are estimated from the operating conditions, and H
The correction injection timing opening ΔIT and the correction cam phase ΔDQN of the oil transfer rate variable mechanism 101 are calculated so that the C / NOx concentration ratio becomes equal to or higher than a predetermined value, that is, the injection timing delay angle and the injection rate reduction amount are calculated. Set and proceed to step 340.

Corrected injection timing opening ΔIT, corrected cam phase Δ
The DQN stores the data shown in FIGS. 29 and 30 in the ROM 122 based on the engine speed Ne and the basic injection amount QN, and reads the data.

Then, in step 340, QN, ITN
From + ΔIT, WN, STEPN, DQN + ΔDQN,
The fuel injection amount Q, the injection timing IT, the opening W of the intake throttle valve 57, the step number STEP of the step motor 59 of the negative pressure control valve 56, and the cam phase DQ of the oil transfer rate variable mechanism 101 are obtained and output.

That is, when the catalyst 51 is at the activation temperature while the generation of NOx is suppressed by the exhaust gas recirculation, the fuel injection timing is retarded so that the HC / NOx concentration ratio in the exhaust gas becomes a predetermined value or more. At the same time, the fuel injection rate (oil feed rate) is reduced.

When the fuel injection rate is reduced, NO in the exhaust gas is reduced.
The x concentration and the HC concentration are reduced as shown in FIG.

Therefore, due to the retard of the fuel injection timing, H
When the C / NOx concentration ratio is set to be equal to or higher than the predetermined value, the retardation width can be reduced, thus improving fuel efficiency.

22 and 27, the exhaust gas recirculation amount may be increased.

[0107]

As described above, according to the present invention, in the exhaust control device provided with the catalyst capable of reducing NOx in the exhaust atmosphere of the diesel engine, the exhaust gas recirculation increase control, the fuel injection timing retard control, and the fuel injection are performed. Since the HC / NOx concentration ratio in the exhaust gas is controlled to a predetermined value or more by the rate reduction control, a high reduction rate of NOx in the catalyst can be secured, and accurate control of the HC / NOx concentration ratio is possible. NOx can be reduced sufficiently. Further, the system is simplified, the cost does not increase, and the fuel consumption does not deteriorate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention.

FIG. 2 is a configuration diagram of the present invention.

FIG. 3 is a configuration diagram of the present invention.

FIG. 4 is a cross-sectional view of the structure of an exhaust system.

FIG. 5 is a sectional view of a negative pressure control valve.

FIG. 6 is a characteristic diagram of a spring load.

FIG. 7 is a sectional view of a fuel injection pump.

FIG. 8 is a cross-sectional view of an oil feeding rate variable mechanism.

FIG. 9 is a front view of an oil feeding rate variable mechanism.

FIG. 10 is a block diagram of a control unit.

FIG. 11 is a characteristic diagram of control data.

FIG. 12 is a characteristic diagram of control data.

FIG. 13 is a characteristic diagram of control data.

FIG. 14 is a characteristic diagram of control data.

FIG. 15 is a characteristic diagram of control data.

FIG. 16 is a flowchart showing control contents.

FIG. 17 is a characteristic diagram of control data.

FIG. 18 is a characteristic diagram of control data.

FIG. 19 is a characteristic diagram of exhaust concentration.

FIG. 20 is a characteristic diagram of exhaust gas concentration.

FIG. 21 is a characteristic diagram of exhaust concentration.

FIG. 22 is a flowchart showing control contents.

FIG. 23 is a characteristic diagram of control data.

FIG. 24 is a characteristic diagram of exhaust concentration.

FIG. 25 is a characteristic diagram of exhaust gas concentration.

FIG. 26 is a characteristic diagram of exhaust concentration.

FIG. 27 is a flowchart showing control contents.

FIG. 28 is a characteristic diagram of an example of control data.

FIG. 29 is a characteristic diagram of an example of control data.

FIG. 30 is a characteristic diagram of an example of control data.

FIG. 31 is a characteristic diagram of exhaust concentration.

FIG. 32 is a characteristic diagram showing the relationship between the HC / NOx concentration ratio and the NOx reduction rate.

[Explanation of symbols]

 50 exhaust gas recirculation device 51 catalyst 52 exhaust passage 53 intake passage 54 exhaust gas recirculation passage 55 exhaust gas recirculation valve 56 negative pressure control valve 57 intake throttle valve 59 step motor 61 diaphragm 62 exhaust pressure chamber 63 intake pressure chamber 64 set spring 65 valve body 67 intake Introducing port 80 Auxiliary spring 86 Step motor 90 Fuel injection pump 91 Cam 92 Plunger 95 Control sleeve 98 Position control mechanism 99 Rotation control mechanism 100 Injection nozzle 101 Oil feed rate variable mechanism 108 Control valve 120 Control unit 125 Engine speed sensor 126 Open accelerator Degree sensor 127 Intake temperature sensor 128 Exhaust temperature sensor 129 Intake pressure sensor 130 Water temperature sensor 131 Fuel temperature sensor 132 Catalyst temperature sensor

Claims (3)

[Claims] 1. An exhaust gas recirculation control means for detecting an operating condition of an engine and an exhaust gas recirculation passage for recirculating a part of exhaust gas from an exhaust passage of the engine to an intake system. In a diesel engine that controls the amount of exhaust gas recirculation from the recirculation passage, a catalyst that can reduce NOx in the exhaust atmosphere of the diesel engine is interposed downstream of the exhaust passage,
Means for detecting the catalyst temperature, exhaust concentration estimating means for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine, and HC and NOx in the exhaust when the catalyst temperature is above a predetermined value. And an exhaust gas recirculation correction control means for increasing and correcting the amount of exhaust gas recirculation from the exhaust gas recirculation passage so that the concentration ratio of Eq. 2. A means for detecting an operating condition of an engine, an injection timing control means for controlling a fuel injection timing of a fuel injection pump based on the operating condition of the engine, and an intake system for a part of exhaust gas from an exhaust passage of the engine. In an exhaust atmosphere of a diesel engine downstream of the exhaust passage, in a diesel engine provided with an exhaust recirculation passage that recirculates into the Means for detecting the catalyst temperature by interposing a catalyst capable of reducing NOx, exhaust concentration estimating means for estimating the concentration of HC and NOx in the exhaust from the operating conditions of the engine, and the catalyst temperature is set to a predetermined value. An injection timing correction control means for retarding the fuel injection timing of the fuel injection pump so that the concentration ratio of HC and NOx in the exhaust becomes a predetermined value or more when the value is equal to or more than the value. Exhaust control device for diesel engine. 3. A means for detecting an operating condition of the engine, an injection timing control means for controlling a fuel injection timing of a fuel injection pump based on the operating condition of the engine, a variable mechanism of a fuel injection rate, and an exhaust passage of the engine. An exhaust gas recirculation passage that recirculates a part of the exhaust gas to the intake system, and an exhaust gas recirculation control unit that controls the amount of exhaust gas recirculation from the exhaust gas recirculation passage based on the operating conditions of the engine. Exhaust concentration estimation for estimating the HC concentration and NOx concentration in the exhaust from the means for detecting the catalyst temperature by installing a catalyst capable of reducing NOx in the exhaust atmosphere of the diesel engine downstream, and operating conditions of the engine When the catalyst temperature is equal to or higher than a predetermined value, the fuel injection timing of the fuel injection pump is retarded and the fuel injection rate is reduced so that the concentration ratio of HC and NOx in the exhaust gas is equal to or higher than the predetermined value. An exhaust emission control device for a diesel engine, comprising: an injection correction control means for performing a decrement correction.